In October 2008, US Customs and Border Protection agents at John F. Kennedy International Airport in Queens, New York, seized a suspicious postmarked container shipped from Nigeria. Moments later, at the airport’s Centers for Disease Control New York Quarantine Station, personnel in full protective gear gingerly opened the package and pulled out dark, misshapen objects—hunks of meat. They photographed and cut off a sample from each, placing them into a container of liquid nitrogen. The remaining meat was incinerated.

In the following 2 years, US Customs confiscated an additional seven postal shipments at JFK and seized 20 more packages straight out of the arms of passengers at four other US airports. Some of the meat was dried, some smoked, some still raw and dripping blood.

This bizarre sting operation was part of a pilot program run by the CDC, the Wildlife Conservation Society, the EcoHealth Alliance, and other institutions to assess the risk of dangerous pathogens entering the country via the illegal wildlife trade (PLoS One, 7:e29505, 2012). Nearly 75 percent of emerging infections—SARS, HIV, Ebola, and more—originate in nonhuman animals, mostly wildlife, says Kristine Smith, the EcoHealth Alliance veterinarian who led the study. And the United States is the number-one importer of live wildlife and wildlife products. Approximately 1.5 billion live wild animals were legally imported into the country between 2000 and 2006, but no one knows the scope of illegal game imports.

The frozen samples collected between 2008 and 2010 were identified and analyzed by researchers at the CDC National Center for HIV/AIDS and Columbia University’s Center for Infection and Immunity. Since investigators couldn’t determine the species of many of the specimens by sight, the team used DNA barcoding—a popular way to identify a species using only a tiny snippet of one mitochondrial gene—to ID 9 primates and 35 rodents, including some threatened and endangered species. But the scientists were less concerned with the species of the tissue samples and more worried about potentially lethal hitchhikers lurking in their cells.

The team screened the meat for multiple pathogens and got unsettling results: the rodents were free of viruses, but half of the primate samples were riddled with simian foamy virus (SFV), cytomegaloviruses, and lymphocryptoviruses, all of which can pose a threat to humans. Scientists have already documented that SFV, which is related to HIV, can cross over into human populations, though those infected with the virus have not become ill. The finding implies that other, more virulent simian viruses could also reside in imported bushmeat, says William Switzer, a retro-virologist at the CDC who screened the meat for SFV. “This is a way for viruses to bypass human carriers and go directly into a biomaterial to expose people in distant locations,” he says. “I believe if we had tested a larger number of confiscations, we would have found more of these known pathogens,” Smith says.

That viruses are present in the imported meat is not surprising, says Mark Woolhouse, a professor of infectious disease epidemiology at the University of Edinburgh in Scotland, who was not involved in the study. “But this is the first time it’s been properly demonstrated in a systematic way,” he says.

The researchers did not assess how efficiently the viruses could infect human cells, but the spread of infections to humans via the animal trade is well documented. In June 2003, 93 cases of monkeypox in the United States were traced to contact with prairie dogs that got the virus from an imported Gambian giant rat. In 2007, an outbreak of bird flu at farms in the United Kingdom was traced to imported Hungarian poultry. “This is not just a theoretical possibility,” says Woolhouse. “This is a cause for concern.”

The pilot project has since expanded to 12 US airports, but the scope of the problem—just how much illegal meat is imported and what types of viral stowaways are onboard—remains unknown. “We just don’t know how often this is happening,” says Switzer. “We may be seeing just the tip of the iceberg.” As sequencing technologies become cheaper, the possibility of wider surveillance of both the legal and illegal animal trade will be more feasible, says Woolhouse. But random screening alone isn’t going to solve the problem. Instead, the animal trade needs regulation to ensure that only healthy, disease-free animals pass from country to country. “There really hasn’t been a big push for this in the international arena,” says Woolhouse. “This is a wake-up call that it needs to happen.”

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Do predators at the tops of food chains have more effective immune systems than other animals?Â It would seem likely.Â After all, they have been eating "bush meat" for thousands of years.

Then again, for whatever reasons, they do not tend to have life spans as long as some non-predatory species.Â Could it be that there is any trade-off involved?Â Could it be, for example, that the overall physiology of lions spends so much energy on putting up a top notch immune system that "burns out" earlier, on average, than members of other species do?

This question is a brainstorming question, and is not meant to offer an argument for or against any position.Â It's a question aimed only at possibly provoking thought among immunologists.

Have comparisons been made between the immune systems of predators which, at the tops of food chains, may have to cope with pathogens (as well as toxins) that may be passed along by every species consumed along the way from bottom to top?

If there are some advantageous differences, the next question that could be asked is:Â What genetic and epigenetic factors are involved in (if there be any) tweaking such immunological systems?

Surely someone has done some interesting research on these questions.Â But how likely is it that studies of top predators' immune systems have been compared alongside human immune systems, and analyzed for any life span-impacting differences?

There is a big difference between contracting a disease from a wildlife pet and bushmeat -- you don't kiss the meat, which is in any case not pumping out virus by aerosol, and I believe most bushmeat will be cooked, which will degrade a lot of its viral load, not eaten raw.

"Approximately 1.5 billion live wild animals were legally imported into the country between 2000 and 2006".Â Is this number correct?Â Seems awfully high to me.Â Why are this many wild animals being imported?Â Are they referring to animals used for farms, food, and medical research as "wild"?

Thanks for your comment, Frank. Indeed 1.5 billion seems like a high number, but it is correct. From the PLoSone study cited in the story: "The United States is one of the world's largest consumers of imported wildlife and wildlife products [5]. Between 2000 and 2006, approximately 1.5 billion live wild animals (around 120,000,000 per year) were legally imported into the United States nearly 90% of which were destined for the pet industry [6], and an average of over 25 million kilograms of non-live wildlife enter the United States each year [5]."

Do predators at the tops of food chains have more effective immune systems than other animals?Â It would seem likely.Â After all, they have been eating "bush meat" for thousands of years.

Then again, for whatever reasons, they do not tend to have life spans as long as some non-predatory species.Â Could it be that there is any trade-off involved?Â Could it be, for example, that the overall physiology of lions spends so much energy on putting up a top notch immune system that "burns out" earlier, on average, than members of other species do?

This question is a brainstorming question, and is not meant to offer an argument for or against any position.Â It's a question aimed only at possibly provoking thought among immunologists.

Have comparisons been made between the immune systems of predators which, at the tops of food chains, may have to cope with pathogens (as well as toxins) that may be passed along by every species consumed along the way from bottom to top?

If there are some advantageous differences, the next question that could be asked is:Â What genetic and epigenetic factors are involved in (if there be any) tweaking such immunological systems?

Surely someone has done some interesting research on these questions.Â But how likely is it that studies of top predators' immune systems have been compared alongside human immune systems, and analyzed for any life span-impacting differences?

There is a big difference between contracting a disease from a wildlife pet and bushmeat -- you don't kiss the meat, which is in any case not pumping out virus by aerosol, and I believe most bushmeat will be cooked, which will degrade a lot of its viral load, not eaten raw.

"Approximately 1.5 billion live wild animals were legally imported into the country between 2000 and 2006".Â Is this number correct?Â Seems awfully high to me.Â Why are this many wild animals being imported?Â Are they referring to animals used for farms, food, and medical research as "wild"?

Thanks for your comment, Frank. Indeed 1.5 billion seems like a high number, but it is correct. From the PLoSone study cited in the story: "The United States is one of the world's largest consumers of imported wildlife and wildlife products [5]. Between 2000 and 2006, approximately 1.5 billion live wild animals (around 120,000,000 per year) were legally imported into the United States nearly 90% of which were destined for the pet industry [6], and an average of over 25 million kilograms of non-live wildlife enter the United States each year [5]."

Hmm....Couple of points.1)Â This phrase from the referenced article "Between 2000 and 2006, approximately 1.5 billion live wild animals (around 120,000,000 per year)" doesn't really inspire much confidence in the care that the PLoSone authors took in writing their article.2)Â Re: the 1.5 billion number, that might be correct, but the source of this article indicates that 96% of the imports were fish or crustaceans, mostly designated as pets.Â Now I know that turtles can carry salmonella, but I'm not aware of tropical fish "pets" as being a significant reservoir for zoonotic diseases.

This is indeed a wake up call for all, especially in countries where bushmeat trading is part of our daily lives. It is a genuine concern and all authorities in both importing and exporting countries need to "gradually" talk their governments into making the trade safe. The sooner we start, the better for all.

Hmm....Couple of points.1)Â This phrase from the referenced article "Between 2000 and 2006, approximately 1.5 billion live wild animals (around 120,000,000 per year)" doesn't really inspire much confidence in the care that the PLoSone authors took in writing their article.2)Â Re: the 1.5 billion number, that might be correct, but the source of this article indicates that 96% of the imports were fish or crustaceans, mostly designated as pets.Â Now I know that turtles can carry salmonella, but I'm not aware of tropical fish "pets" as being a significant reservoir for zoonotic diseases.

This is indeed a wake up call for all, especially in countries where bushmeat trading is part of our daily lives. It is a genuine concern and all authorities in both importing and exporting countries need to "gradually" talk their governments into making the trade safe. The sooner we start, the better for all.